Design and synthesis of 1,10-phenanthroline based Zn(II) complexes bearing 1D push-pull NLO-phores for tunable quadratic nonlinear optical properties

Three Zn(II) complexes bearing 1,10-phenanthroline and one-dimensional (1D) push-pull NLO-phores with various acceptor strength as well as π-conjugation length have been synthesized in high yields for two-dimensional (2D) nonlinear optical response. The quadratic optical nonlinearity of the ligands and the complexes are measured by the HRS technique. The ligands show small second-order optical nonlinearity (β) comparable to the standard, para-nitroaniline (pNA). However, upon complexation with Zn(II), each complex exhibits large β values showing the importance of metal ion in enhancing the optical nonlinear effect.     

Measurement of surface figure of plane optical surfaces using Fizeau interferometer with wedge phase-shifter

A Fizeau interferometer-based set-up for measurement of surface figure of plane optical surfaces has been discussed. Phase-shifting interferometry has been applied using wedge phase shifter. Technique for elimination of system aberrations has been described. Results are shown for a plane surface.     

Bayesian estimation of system reliability in Brownian stress-strength models

A stress-strength system fails as soon as the applied stress,X, is at least as much as the strength,Y, of the system. Stress and strength are time-varying in many real-life systems but typical statistical models for stress-strength systems are static. In this article, the stress and strength processes are dynamically modeled as Brownian motions. The resulting stress-strength system is then governed by a time-homogeneous Markov process with an absorption barrier at O. Conjugate as well as non-informative priors are developed for the model parameters and Markov chain sampling methods are used for posterior inference of the reliability of the stress-strength system. A generalization of this model is described next where the different stress-strength systems are assumed to be exchangeable. The proposed Bayesian analyses are illustrated in two examples where we obtain posterior estimates as well as perform model checking by cross-validation.     

Catalytic effect of molecular iodine in Diels–Alder reaction: a density functional theory study

We explore here the feasibility of employing molecular iodine as Lewis acid catalyst for Diels–Alder (DA) reaction using conceptual density functional theory (DFT) based reactivity indices and transition state analysis at the DFT (B3LYP)/6-31G(d) level of theory. Catalytic effect of iodine is probed using reactivity indices considering six different substituents for the diene at the 2-position and five different substituents at the 1-position of the olefinic dienophile. Comparison of HOMO diene–LUMO dienophile gap between the catalyzed and uncatalyzed processes confirms catalytic effect of iodine in DA reaction. Mechanistic details of both the uncatalyzed and the iodine catalyzed processes is achieved through transition state analysis for four possible stereoisomeric reactive channels with respect to isoprene–acrolein model reaction. A significant cutback in activation barrier is observed in presence of iodine. Influence of iodine on regioselectivity of the reaction and asynchronicity of bond formation is analyzed using local version of the HSAB principle and philicity index.     

Remodeling of the Fibrillation Pathway of α-Synuclein by Interaction with Antimicrobial Peptide LL-III

Liquid-liquid phase separation (LLPS) has emerged as a key mechanism for intracellular organization, and many recent studies have provided important insights into the role of LLPS in cell biology. There is also evidence that LLPS is associated with a variety of medical conditions, including neurodegenerative disorders. Pathological aggregation of α-synuclein, which is causally linked to Parkinson's disease, can proceed via droplet condensation, which then gradually transitions to the amyloid state. We show that the antimicrobial peptide LL-III is able to interact with both monomers and condensates of α-synuclein, leading to stabilization of the droplet and preventing conversion to the fibrillar state. The anti-aggregation activity of LL-III was also confirmed in a cellular model. We anticipate that studying the interaction of antimicrobial-type peptides with liquid condensates such as α-synuclein will contribute to the understanding of disease mechanisms (that arise in such condensates) and may also open up exciting new avenues for intervention.     

Photoacidic behavior of small phenolics in micellar media

The present work demonstrates the photophysical characterization of the interaction of two antibacterial and antimicrobial compounds, thymol and its isomer, carvacrol with different biomimetic micellar nanocavities having varying surface charge characteristics. These types of molecules are reported to be photoacids and this behavior is remarkably exhibited upon interaction with the macromolecular assemblies of micellar systems in the presence of inorganic and organic quencher molecules (silver nitrate and diethylamine) and is manifested through significant modulations of the bimolecular quenching constant values.     

Measurement of surface figure of plane optical surfaces with polarization phase-shifting Fizeau interferometer

A Fizeau interferometer based set up for measurement of surface forms of plane optical surfaces has been discussed. Phase shifting interferometry has been applied using polarization phase shifter. A linearly polarized (632.8 nm) He–Ne laser has been used as the source. Light reflected from the object and the reference/master surfaces are made circularly polarized in opposite senses by means of two properly oriented quarter wave retardation plates placed at appropriate positions, one inside and other outside the interference cavity of the interferometer, and phase shifts are introduced between the object and the reference/master waves by varying angular orientation of a polarizer/analyzer. Final result is made free from any residual wave-front aberrations introduced by the (intra-cavity) wave plate by subtracting phase values obtained by PSI technique between a high optical quality master surface and the reference surface from that obtained for the test object surface with respect to the same reference surface for each point of the interference field. Results are shown for a plane surface.Advantages of the technique presented are linearity and high accuracy in phase stepping, no perturbation of the interference cavity during the phase shifting and possibility of real time or dynamic interferometry.     

Modulation of the Conformational Space of SARS-CoV-2 RNA Quadruplex RG-1 by Cellular Components and the Amyloidogenic Peptides α-Synuclein and hIAPP

Given the emergence of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), which particularly threatens older people with comorbidities such as diabetes mellitus and dementia, understanding the relationship between Covid-19 and other diseases is an important factor for treatment. Possible targets for medical intervention include G-quadruplexes (G4Qs) and their protein interaction partners. We investigated the stability and conformational space of the RG-1 RNA-G-quadruplex of the SARS-CoV-2 N-gene in the presence of salts, cosolutes, crowders and intrinsically disordered peptides, focusing on α-Synuclein and the human islet amyloid polypeptide, which are involved in Parkinson's disease (PD) and type-II diabetes mellitus (T2DM), respectively. We found that the conformational dynamics of the RG-1 G4Q is strongly affected by the various solution conditions. Further, the amyloidogenic peptides were found to strongly modulate the conformational equilibrium of the RG-1. Considerable changes are observed with respect to their interaction with human telomeric G4Qs, which adopt different topologies. These results may therefore shed more light on the relationship between PD as well as T2DM and the SARS-CoV-2 disease and their molecular underpinnings. Since dysregulation of G4Q formation by rationally designed targeting compounds affects the control of cellular processes, this study should contribute to the development of specific ligands for intervention.